The present invention relates to a support nut provided on the threaded spindle shaft of a threaded spindle-nut drive assembly for reducing vibration in the spindle as the spindle is rotated to axially advance and retract the drive nut also provided on the spindle.
When shafts, axes and, in the present case, screw spindles rotate, natural vibrations are induced in the rotating elongated element when the rotation elongated element reaches a characteristic critical speed of rotation, this critical speed being contingent on the diameter of the rotating elongated element in relation to its length and on the speed at which the rotating elongated element rotates. The smaller the diameter/length ratio, the lower the speed at which the rotating elongated element can be permitted to rotate if the rotating elongated element is to be prevented from reaching its critical speed.
Consequently, the rotational speed of longer spindles must be kept low, and the speed at which the nut moves will therefore be correspondingly slow. In order to enable the rotational speed of screw-spindles to be increased without inducing natural vibrations in them, it is usual at the present time to use support sleeves or collars, the smooth bores of which embrace the spindle and thereby support the spindle against a supporting device of the arrangement, the supporting device normally being a cylinder which coaxially, radially spacedly surrounds the spindle. These conventional support sleeves are moved with the aid of pull-rods, in a manner such that when the nut is located at one terminal position of the machine element, that is longitudinally moved by attachment to a drive nut that is threadedly mounted on the spindle for advancement and retraction as the spindle is rotated and counterrotated one support sleeve is located between the nut and a mutually adjacent end of the cylinder and the other support sleeve is located approximately axially centrally in the cylinder. The two support sleeves are connected together by means of the pull-rods. Thus, when the nut moves in the cylinder as the spindle rotates, the nut will ultimately engage the centre support sleeve so that, upon further rotation of the spindle in the same angular sense, the sleeve and nut will move together during continued movement of the nut. Consequently, this support sleeve, with the pull-rods, will draw with it the end-located support sleeve which will therewith move longitudinally along the cylinder at the spped of the nut, towards the centre of the cylinder, where the support sleeve remains stationed when the nut and the support sleeve coacting therewith reach the opposite terminal position in the cylinder.
Although this known type of support means is relatively simple, it creates a large amount of noise when the arrangement is in operation and causes wear on the screw thread crests of the screw-spindle.